1. Field of the Invention
The present invention relates to an inkjet printer, image processor, and image processing method that form an image on a printing medium with use of a printing head having a nozzle array in which a plurality of nozzles ejecting ink are arrayed.
2. Description of the Related Art
A printing head used in an inkjet type printer may include a variation in ejection characteristics (ejection amount, ejecting direction, and the like) among a plurality of nozzles due to manufacturing errors. If there is such a variation, color difference is likely to occur in a printed image.
Conventionally, it is known that, as processing for reducing such density unevenness, a head shading correction technique as disclosed in Japanese Patent Laid-Open No. H10-13674 (1998) is used. The head shading correction technique is a technique that corrects image data according to information on ejection characteristics of each nozzle.
In the correction technique, a pattern for detecting a variation in ejection characteristics among nozzles is formed on a printing medium by a printing head; then a density of the pattern is read with use of a reader such as a scanner; and on the basis of a result of the reading, ejection characteristics of each of the nozzles are detected. Then, according to the detected ejection characteristics of each of the nozzles, the number of ink dots that are finally printed is increased or decreased for each of the nozzles. This enables a density of an image formed by each of the nozzles to be adjusted.
The conventional head shading correction technique as disclosed in the above Japanese Patent Laid-Open No. H10-13674 (1998) is based on the assumption that the reader reading the pattern formed on the printing medium accurately reads the pattern. However, in an actual reader, a variation or error may occur due to a variation, variation with time, temperature characteristics, or the like of a light source. In such a case, in the conventional head shading correction technique including Japanese Patent Laid-Open No. H10-13674 (1998), there arises a problem that an error or variation of a read value influences a correction value in the head shading correction, and therefore color difference of an image due to a variation in ejection characteristics of a nozzle cannot be adequately corrected.